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Flexibility training: Can we improve the ‘best method’?

Thursday, 18 February 2016

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Improving our flexibility is important so that we can safely compete in sports and complete our daily tasks. It’s of even greater importance in clinical settings where injured, diseased or physically impaired individuals strive to regain normal physical function.

Although there are many different forms of stretching the one with the greatest effect, and the longest name, is proprioceptive neuromuscular facilitation, or PNF, stretching. The most common form of this stretching technique requires us to stretch the muscle then tense it while it’s stretched. For reasons that we still don’t understand this form of stretching leads to significant, immediate gains in flexibility, and is great for eliciting longer-term improvements if the stretching is continued over days or weeks.

Two potential drawbacks of this technique, however are that (1) it requires partner assistance (the partner holds your limb during the stretch while you tense your muscles) and (2) there is a chance of minor muscle injury or post-stretch soreness because of the stress of activating a muscle whilst it’s maximally stretched. 

Researchers at the University of Northampton (led by Dr Tony Kay) and Edith Cowan University (Dr Anthony Blazevich) sought to understand the benefits of PNF stretching as well as to find an easier and potentially safer method of achieving the same results.

Using ultrasound imaging, similar to that used by a clinician to observe an unborn child, they were able to visualise the elongation of the calf muscles and Achilles tendon before and after performing muscle stretches, muscle contractions, and PNF stretching that included both stretches and contractions.

When the muscle was tensed but not stretched, the tendon became less stiff with no change in the muscle, however when the muscle was stretched the muscle became less stiff with no change in the tendon, yet both immediately increased flexibility. After PNF stretching, where the muscle is tensed while it’s stretched (the ankle is rotated so the foot moves up toward the shin while the muscle is voluntarily activated), both the muscle and the tendon became less stiff and crucially, the increases in flexibility were significantly greater. 

These findings were recently published in Medicine & Science in Sports & Exercise and led the research team, which included Dr Anthony Blazevich (ECU), to develop a new variation of PNF where the muscle was tensed in a shortened position after stretching. In a follow-up study, recently published in European Journal of Applied Physiology, identical changes were found in muscle and tendon stiffness as well as flexibility after PNF stretching (where the muscle is tensed while it’s stretched) and after the new variation of PNF (where the muscle was stretched but then the muscle was returned to its resting length before it was tensed).

But, although similar changes in stiffness occurred after both stretches, these changes were not closely related to the changes in flexibility. Instead, significant increases in “stretch tolerance”, the amount of tension in the muscle the subjects can bear during a maximal stretch, were found to be most strongly related to the increases in flexibility. This shows that the stretches affect the nervous system in some way, although we still don’t know the location in the nervous system where this influence occurs.

Nevertheless, this simple change in technique removed the two potential drawbacks of traditional PNF stretching and yet provided identical immediate gains in flexibility.  These findings provide good evidence for the use of a safer but equally effective method of stretching. 

It will be interesting to now examine the long-term effects of this technique so that its chronic effects on flexibility and our ability to perform sporting tasks or activities of daily living can be evaluated.

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